The present invention is based on Japanese Patent Application No. 2001-25591, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an induction heating and fixing device for fixing toner on a recording medium in image forming apparatuses such as copiers, printers, and facsimile machines.
2. Description of the Related Art
In recent years fixing devices using the induction heating method have been used as fixing devices in image forming apparatuses.
For example, U.S. Pat. No. 4,570,044 discloses an induction heating and fixing device wherein a part of an iron core forming a closed magnetic circuit is inserted into the hollow space within a cylindrical fixing roller heated by induction, and a coil is wound around the iron core to generate a magnetic field, such that the fixing roller is heated when an alternating current flows through the coil.
Disadvantages arise, however, in that since this induction heating and fixing device is closed at both ends of the fixing roller heated by induction, the temperature distribution in the axial direction of the fixing roller produces a higher temperature in the center area and lower temperature at both ends due to the greater radiant heat at the ends which easily reduces the temperature and causes a large temperature gradient between the center part and the end parts.
An object of the present invention is to provide an induction heating and fixing device which suppresses temperature drop at the bilateral ends of the fixing roller, and maintains uniform temperature distribution in the axial direction of the fixing roller.
The present invention relates to an induction heating and fixing device comprising:
a hollow cylindrical fixing member heated by induction;
a core for forming a closed magnetic circuit, a part of the core being inserted onto the hollow cylindrical fixing member;
a ring member formed of magnetic material and provided on the core in the vicinity of the bilateral ends of the hollow cylindrical fixing member;
a coil wound around the core; and
a pressure member disposed so as to press against the hollow cylindrical fixing member.